1. Field of the Invention
This invention relates primarily to disk file apparatus of the accessing head type, wherein a magnetic read/write head is movable radially of a recording surface of a rotating magnetic disk for reading or recording data in digital form at selectable radial locations or tracks. The invention relates more particularly to such an apparatus wherein a hollow base is provided and so configured, and a disk/spindle/housing assembly and voice coil motor (VCM) are so mounted therein and thereto, that during VCM operation, bending moments in the base are substantially eliminated and a substantially uniform temperature differential is maintained between the interior and exterior surfaces of the base.
In disk files of the accessing head type, the disks have traditionally been supported on a vertical spindle projecting upwardly from a flat horizontal baseplate; and a carrier/arm assembly has been movable horizontally on the baseplate in response to energization of the coil of a VCM actuator to carry magnetic heads into transducing engagement with a selected track of a particular disk. Reaction to this movement of the heads by the actuator sets up bending moments in the baseplate because the neutral axis of the flat baseplate is below the force center of the VCM and the mass centers of the VCM and of the disk stack. These bending moments can cause dynamic bending of the spindle and track misregistration error. Moreover, since there is a temperature differential between the upper and lower surfaces of the baseplate, the resultant thermal expansion causes static out-of-plane bending of the baseplate.
To reduce this bending, it has been proposed in U.S. Pat. No. 3,768,083 to provide two flat overlying baseplate sections. One is made very rigid and supports the disk pack, magnetic heads, head support and spindle; and the other supports the heavy pole pieces of the VCM. However, there is still out-of-plane bending because the center of force of the VCM and the centers of gravity of the VCM and disks are placed a significant distance from the neutral plane of the baseplate; and distortion still occurs due to the difference in temperature between the upper and lower surfaces of the baseplate.
These problems are substantially eliminated in the disk file embodying the present invention, wherein each VCM actuator is mounted within and supported by a hollow generally ring-shaped symmetrical base as closely as possible to a neutral plane that divides opposing walls of the base into two substantially symmetrical parts; and the disk/spindle/housing assembly is independently secured to the base with its spindle normal to the neutral plane and its center of gravity substantially coincident therewith.
This improved configuration is not disclosed or suggested by the most pertinent prior art known to applicant and to those substantively involved in the preparation of this application. U.S. Pat. No. 4,005,490 shows a cylindrical frame and bridge plates for supporting centrally a disk, spindle and motor in a symmetrical arrangement; however, the motor comprises a rotor surrounding a stator, and only fixed heads are employed, and there is no VCM or equivalent translationally movable actuator mounted as herein described for controlling the heads.
A disk file apparatus marketed by Data Products Corporation has plural access mechanisms mounted on the exterior of a cast metal shroud surrounding disk stack. However, the shroud apparently does not support the disk stack and spindle, which appear to be supported from beneath. Hence, the shroud does not function as a base.
U.S. Pat. No. 4,008,492 discloses a magnetic disk memory device wherein a disk pack is enclosed in a shroud. The shroud has a chamber to which air is supplied to cool the disks to reduce the temperature gradient between components within the chamber. However, this arrangement does not propose a solution to the dynamic out-of-plane bending problem with which applicant is also concerned. The disk file apparatus according to the present invention substantially eliminates both dynamic and static out-of-plane bending of the base.